1. Statement of the Technical Field
The inventive arrangements relate generally to RF devices and more particularly to preventing degradation of fluid dielectric that are used in RF devices.
2. Description of the Related Art
Glass ceramic substrates calcined at 850xcx9c1,000 C are commonly referred to as low-temperature co-fired ceramics (LTCC). This class of materials have a number of advantages that make them especially useful as substrates for RF systems. For example, low temperature 951 co-fire Green Tape(trademark) from Dupont(copyright) is Au and Ag compatible, and it has a thermal coefficient of expansion (TCE) and relative strength that are suitable for many applications. The material is available in thicknesses ranging from 114 xcexcm to 254 xcexcm and is designed for use as an insulating layer in hybrid circuits, multi-chip modules, single chip packages, and ceramic printed wire boards, including RF circuit boards. Similar products are available from other manufacturers.
LTCC substrate systems commonly combine many thin layers of ceramic and conductors. The individual layers are typically formed from a ceramic/glass frit that can be held together with a binder and formed into a sheet. The sheet is usually delivered in a roll in an unfired or xe2x80x9cgreenxe2x80x9d state. Hence, the common reference to such material as xe2x80x9cgreen tapexe2x80x9d. Conductors can be screened onto the layers of tape to form RF circuit elements antenna elements and transmission lines. Two or more layers of the same type of tape is then fired in an oven. The firing process shrinks all of the dimensions of the raw part. Accordingly, it is highly important that the material layers all shrink in a precise, predetermined way that will provide consistent results from one module to the next.
Recent interest in fluid dielectric materials suggest the use of LTCC as a substrate because of its known resistance to chemical attack from a wide range of fluids. The material also has superior properties of wetability and absorption as compared to other types of solid dielectric material. These factors, plus LTCC""s proven suitability for manufacturing miniaturized RF circuits, make it a natural choice for use in RF devices incorporating fluid dielectrics.
Still, the use of fluid dielectrics raises new potential problems. For example, fluid dielectrics can suffer degradation from a variety of factors. For example, the degradation can occur due to temperature variations, micro-gravity, phase separation, particulate settling and orientation, ionic migration, dendritic growth, and other intrinsic molecular separation phenomena. Some of these problems are less likely to occur in dynamic systems. However, even in the case of dynamic systems, fluids can separate due to particle fallout, particle separation, sedimentation, eddy effects and so on. These kinds of fluid degradations will effect the overall electrical characteristics of the fluid dielectric, regardless of whether the fluid is a dielectric suspension, dielectric agglomerate, a dielectrically loaded fluid, or a polymer blend.
The invention concerns a method for preventing degradation of a fluid dielectric in an RF device. The method can include the steps forming a substrate of the RF device from a low temperature co-fired ceramic (LTCC), positioning within a cavity structure of the substrate at least one fluid dielectric, and agitating the fluid dielectric with a piezoelectric device. According to one aspect of the invention, the piezoelectric device can be formed from lead zirconate titanate (PZT) component. According to another aspect of the invention, the piezoelectric device can be in direct contact with the fluid dielectric. Also, at least one electrical contact can be provided in the substrate and coupled to the PZT for applying an exciter voltage.
The method can also include the step of bonding the PZT to the substrate. The bonding step can be performed by positioning the PZT in contact with the substrate and co-firing the substrate together with the PZT. The PZT can be elementally doped to enhance embedded interstitial bonding with the substrate. For example, the PZT can be doped with calcium, lead, zirconium, oxygen, titanium, or a rare earth element selected from the group consisting of Ruthenium, Osmium, Rhenium, Halfnium, Tantalum, and Germanium. The doping level can be advantageously selected to be in the range from between about 0.5 to 18 percent weight of the PZT
The invention can also include an RF device that includes a substrate formed of a low temperature co-fired ceramic (LTCC). A cavity structure can be formed within the substrate and at least one fluid dielectric can be contained within the cavity structure. Further, a piezoelectric device can be provided for agitating the fluid dielectric. The piezoelectric device can be in direct contact with the fluid dielectric. The RF device can also include at least one electrical contact formed in the substrate and coupled to the PZT for applying an exciter voltage.
According to one aspect, the piezoelectric device can be comprised of lead zirconate titanate (PZT) that is bonded to the substrate. The PZT and the substrate can be advantageously co-fired together. The PZT can also be doped to enhance embedded interstitial bonding with the substrate. For example, the PZT can be doped with calcium, lead, zirconium, oxygen, titanium, or a rare earth element selected from the group consisting of Ruthenium, Osmium, Rhenium, Halfnium, Tantalum, and Germanium. In any case, the dopant material can comprise between about 0.5 to 18 percent weight of the PZT.